How Do You Test Your Add-Ons?

I finally am sitting down to write the add-ons I have had planned for quite some time now but I am curious about testing methods. So I’m looking to see what method you use to develop and test your add-ons.

A few things that come to are:

1. Protecting the “integrity” of the database (i.e bad MySQL queries and etc.)
2. Testing in different versions of EE
3. Any other tips or “gotch-yas” you might have experienced?

On a side note, I love ExpressionEngine but I have always found the development documentation to be somewhat lacking. I know others feel this way as well. Being new to development having a great set of docs can make or break it for me.